From http://www.imiscommunity.com/turning_off_smart_quotes_in_outlook_2007

Turning Off Smart-Quotes in Outlook 2007
Posted February 7th, 2008 by Paul Bradshaw

I typically find myself typing actual code into many emails, and find that Outlook always replaces my single and double quotes with the curley “smart-quotes”. This makes cutting/pasting without syntax errors difficult. So after a little digging, I found out how to turn smart-quotes off in Outlook 2007: 1. In the main Outlook window, on the Tools menu, click Options.
2. In the Options dialog box, click the Mail Format tab, and then click Editor Options.
3. In the Editor Options dialog box, click Proofing, and then click AutoCorrect Options.
4. In the AutoCorrect dialog box, do the following: Click the AutoFormat As You Type tab, and under Replace as you type, select or clear the “Straight quotes” with “smart quotes” check box. Click the AutoFormat tab, and under Replace, select or clear the “Straight quotes” with “smart quotes” check box.